1. Field of the Invention
This invention relates to semiconductor devices, and more specifically to integrated circuits, hereinafter referred to as chips, and the process in which electrical connections for their use are formed on a thin metallic layer attached to a flexible insulating strip, hereinafter referred to as film.
2. Description of the Prior Art
In the production of semiconductor devices processes have been developed to permit mass production of the electrical connections (leads) necessary for their use, see U.S. Pat. No. 3,440,027 issued Apr. 22, 1969. Presently the two major processes (wet film and dry film) both involve the use of a flexible insulating strip that is clad with a thin metallic layer on one side. The metal, usually a thin strip of copper, is prepared to allow a photographic process to imprint the integrated circuit lead pattern desired (positive photographic method) or a pattern excluding the integrated circuit lead pattern desired (negative photographic method) on the treated metallic surface. The imprinted pattern is then developed and the metallic surface subjected to an etching material to etch away all the metal in the strip except for the desired beam lead pattern, see U.S. Pat. No. 3,777,365 issued Dec. 11, 1973.
The leads generally converge towards the center of the metallic layer opposite which is usually an aperture through the strip to facilitate bonding of the chip to the leads. This aperture, called a personalty window, must be sealed prior to application of the etching material in order to prevent undercutting of the leads by the etching agent, and at the same time can support the leads until just prior to bonding of the chips. Undercutting, as used in a method of chip lead fabrication utilizing an etching process, denotes action by the etching material on the individual leads causing the leads to lack a uniform cross-sectional area from the side of the metallic strip which was imprinted to the side adjacent to the insulating strip.
Preparation of wet film for the photographic process is a slow and labor consuming operation requiring precise control of ambient conditions. The dry film process on the other hand is inherently much faster but the cost of preparing the film for the lead fabrication is more costly. Both wet and dry film processes for fabricating chip lead patterns normally use film with precut apertures in the insulating strip. It is possible, however, to assemble chips to their lead structures without prior cutting of the aperture in the insulating strip or by etching an aperture in the film after the lead pattern has been fabricated.
At present the apertures are sealed by a fluid applied by either a spray or roller application or by dripping drops of fluid onto the back side of the metallic strip. Problems are encountered, however, when the process is sped up as an uneven coat or lack of complete aperture seal may occur. An uneven coat causes problems in the developing process which may require that the fluid be applied only after the imprinted pattern has been developed. This additional handling process occurs at a critical time in the overall process since small scratches on the metallic surface can ruin the entire lead pattern.
In general it is an object of the present invention to provide a device to overcome the above named disadvantages in the fabrication of electrical connections for integrated circuits.
Another object of the invention is to cover the aperture in the insulating strip to prevent undercutting during the etching process.
Another object of the invention is to speed up the aperture sealing process.
Another object of the invention is to reduce the number of different steps used in processing the film.
Another object of the invention is to allow application of a more uniform layer of sealing material to the insulating strip.
These and other objects of the invention will become apparent to one of ordinary skill in the art when viewed in light of the detailed drawings and their description.